1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and specifically, to an ink jet recording apparatus in which an image is recorded by jetting droplets onto a recording medium based on image information.
2. Description of the Related Art
Japanese Patent Application Laid-Open (JP-A) Nos. 10-6521 and 10-114084 disclose an ink jet recording apparatus which includes a sub-ink tank provided at a recording head, a main tank for supplying ink to the sub-ink tank, and an ink sensor for detecting the amount of ink in the sub-ink tank. When the ink sensor detects that the amount of ink in the sub-ink tank is the lower limit or less, ink is supplied from the main tank to the sub-ink tank.
When other operations are stopped in order to supply ink, efficiency decreases. Therefore, JP-A No. 10-315493 discloses an ink jet image forming apparatus in which the other operations can continue even while ink is supplied. The ink jet image forming apparatus is constructed to supply ink only at a fixed time: before conversion of image data ends or after image formation. Ink supplying occurs during a time period where it is possible to sufficiently fill the sub-ink tank, regardless of whether this time period is during the image data conversion or after the image formation.
JP-A No. 11-227220 discloses an ink jet recording apparatus in which the amount of ink jetted and discharged from a head portion is calculated, and the amount of ink to be supplied is controlled in accordance with the results of the calculation or the results of detecting the level of the ink surface in a sub-ink tank by a float.
JP-A No. 11-58768 discloses an ink jet recording apparatus which includes an ink amount sensor mounted to an ink tank for detecting the amount of ink in the ink tank. When shortage of ink is detected by the ink amount sensor during printing, the number of passes and the number of pages are determined based on the detection results, and ink is supplied to the ink tank after a predetermined printing processing.
JP-A Nos. 10-6521 and 10-114084 do not, however, clearly specify when the amount of ink in the sub-ink tank is detected. Therefore, when ink is to be supplied during a printing processing, it is necessary to slow down or stop the printing processing first and then supply ink in order to maintain print quality. As a result, the printing speed decreases. Further, when the level of the ink in the sub-ink tank does not reach a predetermined position, it is determined that ink in the main tank has run out. This means that ink supply operations are performed more than necessary. Thus, it takes a long time before it is determined that ink in the main tank has run out.
Moreover, in the structure of the ink jet image forming apparatus disclosed in JP-A No. 10-315493, when an insufficient amount of ink is detected during execution of a print job including a plurality of pages, ink can only be supplied during image data conversion. Therefore, a printing operation for a subsequent page may be implemented without a sufficient amount of ink being supplied to the sub-ink tank, and ink may run out before printing of the subsequent pages is finished. Further, ink is supplied after image formation, thereby decreasing the printing speed.
JP-A No. 10-315493 also discloses a structure in which ink is supplied during image formation and ink supplying continues for a predetermined time even after the image formation. In this structure, however, the standby time between printing of a page and printing of a subsequent page becomes long. As a result, a problem arises in that the printing speed decreases.
In the ink jet recording apparatus disclosed in JP-A No. 11-227220, when the amount of ink to be jetted varies with the environment, the amount of ink to be jetted becomes smaller or larger than the amount of ink actually jetted. As a result, the amount of ink supplied varies, and ink cannot be supplied in accordance with preset values. Further, since the amount of ink to be supplied is controlled by the float, ink supplying operations continue even if no ink is in the main tank.
In the ink jet recording apparatus disclosed in JP-A No. 11-58768, the number of pages which can be printed is determined based on the amount of ink in the ink tank, which amount is detected by the ink amount sensor. After a predetermined printing processing is finished, ink is supplied based on the determination result. However, in order to determine the number of pages which can be printed, not only whether the amount of ink in the ink tank is no more than a predetermined amount but also the amount of ink actually remaining in the ink tank need to be detected. Therefore, a problem arises in that the ink amount sensor is expensive. Further, in the case of printing an image which requires an ink amount equal to or larger than the amount of ink actually remaining in the ink tank, a problem of image defects arises since ink is not supplied to the ink tank during printing.
As described above, in the conventional ink jet recording apparatuses, the amount of ink in the ink tank for supplying ink to the recording head is detected, and when the amount is the lower limit or less, a signal indicating shortage of ink in the ink tank is outputted. When the amount of ink in the ink tank is insufficient, ink is supplied from a separate ink supply tank. However, since control of the timing of the ink supplying is insufficient, problems may arise in that image defects are caused due to shortage of ink in the ink tank and the printing speed decreases.
In order to achieve the above object, a first aspect of the present invention is an ink jet recording apparatus comprising: a recording head including an ink tank for storing ink, the recording head being driven and controlled based on image information so as to jet onto a recording medium ink supplied from the ink tank; detecting means for detecting the amount of ink remaining in the ink tank; supply means including a main tank for storing ink, the supply means supplying ink from the main tank to the ink tank when the recording head is disposed at an ink supplying position; and control means for controlling the supply means so that, when the remaining ink amount detected by the detecting means is above a lower limit, ink is supplied during non-recording time in an amount corresponding to the amount of ink used.
In this structure, when the remaining ink amount detected by the detecting means is above the lower limit of the ink in the ink tank, the control means controls the supply means so that ink is supplied from the main tank to the ink tank, which is disposed at the ink supplying position during non-recording time, in an amount corresponding to the amount of ink used. Non-recording time described herein (or during non-printing operations which will be described later) refers to time other than the time ink is jetted onto the recording medium, and typically refers to the time between recording jobs, the standby time for recording, or the preparation time for recording. Ink may be supplied during a job as long as the ink supply does not delay recording, and the non-recording time may be any length of time as long as it does not delay recording. Namely, ink is supplied to the ink tank during non-recording time in an amount corresponding to the amount of ink which has been used. Thus, the time the ink amount reaches the lower limit can be delayed. Further, image defects caused by shortage of ink, and decreases in the recording speed can be prevented. As a result, it is possible to significantly decrease the probability of recording being interrupted by shortage of ink.
The control means preferably estimates, based on the image information, the amount of ink used. Since jetting of ink by the recording head is controlled based on image information, the amount of ink used can be easily estimated by, for example, counting the number of pixels corresponding to the amount of ink jetted. This structure is simpler than a structure in which the amount of ink is actually measured. Further, it is preferable that the control means determines whether or not the amount of ink used exceeds a predetermined value, and when the determination is affirmative, the control means controls the supply means during non-recording time so that ink is supplied to the ink tank. The predetermined value preferably corresponds to an amount of ink which can be supplied during non-recording time without interrupting recording. In a preferable aspect, the predetermined value is no more than an upper limit of the ink remaining in the ink tank. In this way, it is possible to prevent a case in which the amount of ink remaining in the ink tank exceeds the upper limit because of errors in estimation of the amount of ink used, which errors are caused by environmental changes. Further, it suffices that the detecting means detects if the amount of ink remaining in the ink tank is above or below the lower limit. Therefore, another detecting means for detecting the upper limit of ink remaining in the ink tank is not necessary. As a result, this structure can be simplified and produced at a low cost. The lower limit is an amount of ink which can be used for a predetermined amount of printing. When the predetermined amount of printing is set as an amount by which predetermined recording quality can be maintained, even after it is detected that the amount of ink remaining in the ink tank is less than the lower limit, recording can be performed while the predetermined recording quality is maintained. The predetermined amount of printing preferably corresponds to the maximum amount of ink assumed to be used or an amount of ink to be used for a job which is frequently executed.
A second aspect of the present invention is an inkjet recording apparatus comprising: an inkjet recording head including an ink tank to which ink is supplied, the ink jet recording head printing by jetting the ink from the ink tank in accordance with image information in a print job; remaining ink amount detecting means for detecting the amount of ink remaining in the ink tank at predetermined time intervals and outputting an empty signal indicating shortage of ink when the ink amount is no more than a lower limit; ink supply means including a main tank for storing ink, the ink supply means supplying ink from the main tank to the ink tank in response to the empty signal outputted from the remaining ink amount detecting means; and control means for controlling the ink supply means such that, when the remaining ink amount detected by the remaining ink amount detecting means is above the lower limit, ink is supplied to the ink tank in an amount corresponding to the amount of ink used.
In the inkjet recording apparatus according to the second aspect, the remaining ink amount detecting means detects the amount of ink remaining in the ink tank at predetermined time intervals and outputs an empty signal indicating a shortage of ink when the remaining ink amount is no more than a lower limit. The ink supply means includes a main tank for storing ink and supplies ink from the main tank to the ink tank in response to the empty signal outputted from the remaining ink amount detecting means. The control means controls the ink supply means so that, when the remaining ink amount detected by the remaining ink amount detecting means at the predetermined time intervals is above the lower limit, ink is supplied to the ink tank in an amount corresponding to the amount of ink which has been used.
Since the ink jet recording apparatus according to the second aspect has the above-described structure, a period between the time ink is supplied to the ink tank to its upper limit and the time the amount of ink in the ink tank is detected can be made long. Further, before the amount of ink in the ink tank reaches the lower limit, ink is supplied to the ink tank in an amount corresponding to the amount of ink which has been used. Thus, a relatively large amount of ink is constantly held in the ink tank. Further, it is possible to lower the possibility of image defects being caused by shortage of ink during a printing processing for a print job which has a large coverage area and thus requires a large amount of ink. Therefore, the probability of the printing processing being interrupted by the ink supply operation significantly decreases, and as a result, throughput can be improved.
It is advantageous if the amount of ink to be supplied which corresponds to the amount of ink used is somewhat smaller than the amount which can be estimated based on the pixel count. Namely, the amount of ink which can be estimated based on the pixel count does not necessarily correspond with the amount of ink actually used. Therefore, it is possible to prevent a problem of oversupply of ink to the ink tank by supplying ink thereto in an amount less than the predetermined amount. An upper limit sensor is preferably provided at the ink tank so as to monitor the amount of ink therein, since ink can be supplied to the ink tank to its upper limit.
A third aspect of the present invention is an ink jet recording apparatus according to the second aspect, wherein the control means controls the ink supply means such that ink is supplied to the ink tank when the print job is not being printed.
According to the third aspect, in the ink jet recording apparatus of the second aspect, the timing of ink supply is limited to the time a print job is not being printed. The time a print job is not being printed refers to the time other than the time a printing processing is carried out, such as the time immediately before or after a printing processing for a print job, the time the power supply is turned on or off, the time a recording medium to be printed such as paper is loaded, and the time the operation mode of the apparatus is switched to sleep mode for power saving. Further, the apparatus can be structured such that a user can specify desired time such as lunch break. Furthermore, a period of time when few printing operations are performed may be automatically detected by the control means based on statistical data, and ink may be supplied during the detected period of time. Since ink is supplied with the above-described timing, the probability of the printing processing for a print job being interrupted by ink supply decreases. Therefore, throughput is substantially improved. Moreover, since ink is not supplied between printing of a page and printing of a subsequent page, it is possible to prevent a case in which a printing processing for a print job is interrupted by an ink supply processing, thereby keeping a user waiting.
A fourth aspect of the present invention is an ink jet recording apparatus according to the second aspect, wherein the remaining ink amount detecting means detects the amount of ink remaining in the ink tank over a first time interval until the ink amount reaches a predetermined amount larger than the lower limit, and detects the remaining ink amount over a second time interval, which is shorter than the first time interval, after the ink amount has reached the predetermined amount.
When the amount of ink in the ink tank is frequently detected, accuracy of detection is improved, but this frequent detection wastes time. Therefore, in the fourth aspect, the amount of ink remaining in the ink tank is detected over a first time interval until the ink amount reaches a predetermined amount which is relatively large, and the remaining ink amount is minutely detected over a second time interval, which is shorter than the first time interval, after the ink amount has reached the predetermined amount. In this way, the number of detection of the amount of ink in the ink tank is minimized.
As a result, the time required for stopping the operation of the apparatus for ink amount detection can be substantially decreased. Further, the amount of ink remaining in the ink tank can be detected immediately after the ink amount has reached the lower limit. The predetermined amount can be appropriately selected.
When a print job includes a large number of sheets, the amount of ink in the ink tank may become insufficient before printing of all the sheets is finished. Therefore, once a predetermined number of pixels is printed, the amount of ink in the ink tank may be detected during a printing processing as well. In this case, the printing processing is interrupted by the detection. Thus, in the case of an ink jet recording apparatus which has ink tanks for multiple colors so that full-color images are formed, it is preferable to detect only the amount of ink in an ink tank for a specific color when the amount of ink used exceeds an amount corresponding to the predetermined number of pixels.
A fifth aspect of the present invention is an ink jet recording apparatus according to the second aspect, wherein the remaining ink amount detecting means detects the remaining ink amount for every predetermined number of printed pixels, the predetermined number of printed pixels being smaller than the number of pixels which can be printed after the empty signal is outputted.
The amount of ink in the ink tank is detected when the remaining ink amount reaches the lower limit. However, even after the remaining ink amount has reached the lower limit, some ink remains in the ink tank. According to the fifth aspect, in the ink jet recording apparatus of the second aspect, the remaining ink amount detecting means detects the remaining ink amount for every predetermined number of printed pixels, which predetermined number of printed pixels is smaller than the number of pixels which can be printed with the ink remaining in the ink tank after the ink amount has reached the lower limit. In this way, a case in which ink in the ink tank runs out during printing so that further printing cannot be performed is prevented. The predetermined number of pixels for the ink amount detection is preferably set on the basis of the coverage area for the best quality. As a result, printing of files having a large coverage area can be ensured.
A sixth aspect of the present invention is an ink jet recording apparatus according to the second aspect, wherein, when the print job is not being printed, the remaining ink amount detecting means controls the amount of ink remaining in the ink tank by the number of pixels corresponding to the amount of ink jetted from the ink jet recording head and detects the remaining ink amount when the number of pixels exceeds a predetermined number.
When the amount of ink in the ink tank is detected directly, the remaining ink amount can be more accurately detected as compared with cases in which the remaining ink amount is detected based on the number of pixels. However, this direct detection takes time. Thus, according to the sixth aspect, in the ink jet recording apparatus of the second aspect, the detection mode is switched such that, when the print job is not being printed, the remaining ink amount detecting means controls the amount of ink remaining in the ink tank by the number of pixels corresponding to the amount of ink jetted from the ink jet recording head and detects the remaining ink amount when the number of pixels exceeds a predetermined number.
Namely, when the amount of ink remaining in the ink tank is relatively large, even if there is an error in the remaining ink amount, the possibility of the ink running out is low. Thus, the remaining ink amount is detected at high speed by calculating the jetted pixels. However, when the amount of ink remaining in the ink tank is relatively small, if there is an error in the remaining ink amount, the possibility of ink running out is high. Therefore, the remaining ink amount is accurately detected by detecting the amount of ink remaining in the ink tank directly. The structure for directly detecting the remaining ink amount is not particularly limited. For example, an optical sensor can be used in which the remaining ink amount is detected by irradiating light onto the level of the ink and measuring the time required for the light to be reflected back to the optical sensor.
By switching the detection mode in the above-described manner, the printing processing can be efficiently carried out. The predetermined number of pixels can be appropriately selected. It is advantageous if the predetermined number of pixels is set to a number of pixels which corresponds to the ink amount near the lower limit of the ink tank.
A seventh aspect of the present invention is an ink jet recording apparatus according to the second aspect, wherein the remaining ink amount detecting means detects the remaining ink amount again after ink has been supplied to the ink tank by the ink supply means in response to the empty signal outputted from the remaining ink amount detecting means, and, when the remaining ink amount detecting means outputs the empty signal again, the control means outputs a main tank empty signal indicating that the main tank is empty.
According to the seventh aspect, in the ink jet recording apparatus of the second aspect, the remaining ink amount detecting means detects the remaining ink amount after ink has been supplied to the ink tank. When the remaining ink amount detecting means outputs the empty signal again, it is determined that ink has not been supplied to the ink tank and that there is no ink in the main tank. With this structure, the amount of ink remaining in the main tank can be detected without using a sensor. Therefore, the apparatus as a whole can be produced at a low cost.
An eighth aspect of the present invention is an ink jet recording apparatus according to the second aspect, further comprising storage means for storing a number of pixels corresponding to the amount of ink jetted from the ink jet recording head, wherein the remaining ink amount detecting means detects the remaining ink amount again after ink has been supplied to the ink tank by the ink supply means in response to the empty signal outputted from the remaining ink amount detecting means, and, when the remaining ink amount detecting means outputs the empty signal again, the control means compares the number of pixels stored in the storage means with the number of pixels corresponding to the amount of ink filled in the main tank and outputs, when the numbers are the same or close to each other, a main tank empty signal indicating that the main tank is empty.
According to the eighth aspect, in the ink jet recording apparatus of the second aspect, after ink has been supplied to the ink tank, the remaining ink amount detecting means detects the amount of ink remaining in the ink tank. When the remaining ink amount detecting means outputs the empty signal again, it can be determined that ink has not been supplied to the ink tank or an ink flow path between the main tank and the ink tank is being interrupted for some reason. Accordingly, the control means compares the number of pixels stored in the storage means with the number of pixels corresponding to the amount of ink filled in the main tank (i.e. the amount of ink in the main tank before a print job). When the numbers are the same or close to each other, it is determined that ink has not been supplied to the ink tank, and that the main tank is empty. Then, the control means outputs a main tank empty signal indicating that the main tank is empty. The ink jet recording apparatus may also be structured such that, when the number of pixels stored in the storage means is significantly different from the number of pixels corresponding to the amount of ink filled in the main tank, it is determined that the ink flow path between the main tank and the ink tank is interrupted, and a warning is given.
With the above-described structure, the amount of ink in the main tank can be detected without using a sensor. Therefore, the apparatus as a whole can be produced at a low cost. Further, problems caused by interruption of the ink flow from the tank or the like can also be found.
In the seventh and eighth aspects, for example, in cases where an upper limit sensor is provided which outputs a signal when ink is not supplied to the ink tank to its upper limit, it can be determined that there is no ink in the main tank when the upper limit sensor outputs a signal after ink has been supplied to the ink tank. Alternatively, in cases where an upper limit sensor is provided which outputs a signal when ink which is supplied to the ink tank reaches its upper limit, it can be determined that there is no ink in the main tank when the upper limit sensor outputs no signal after ink has been supplied to the ink tank.
A ninth aspect of the present invention is an ink jet recording apparatus comprising: an ink jet recording head including an ink tank to which ink is supplied, the ink jet recording head printing by jetting the ink from the ink tank in accordance with image information in a print job; remaining ink amount detecting means for detecting the amount of ink remaining in the ink tank over a first time interval until the ink amount reaches a predetermined amount larger than a lower limit, and for detecting the ink amount over a second time interval, which is shorter than the first time interval, after the ink amount has reached the predetermined amount, and outputting an empty signal indicating shortage of ink when the ink amount is no more than the lower limit; and ink supply means including a main tank for storing ink, the ink supply means supplying ink from the main tank to the ink tank in response to the empty signal outputted from the remaining ink amount detecting means.
According to the ninth aspect, the remaining ink amount detecting means detects the amount of ink remaining in the ink tank over a first time interval until the remaining ink amount reaches a predetermined amount larger than a lower limit, and detects the remaining ink amount over a second time interval, which is shorter than the first time interval, after the remaining ink amount has reached the predetermined amount.
When the amount of ink remaining in the ink tank is frequently detected, accuracy of detection is improved, but this frequent detection wastes time. Therefore, in the ninth aspect, the amount of ink remaining in the ink tank is detected over a first time interval until the ink amount reaches a predetermined amount which is relatively large, and the remaining ink amount is detected over a second time interval, which is shorter than the first time interval, after the ink amount has reached the predetermined amount. In this way, the number of detection of the amount of ink in the ink tank is minimized.
As a result, the time required for stopping the operation of the apparatus for ink amount detection can be substantially decreased. Further, the amount of ink remaining in the ink tank can be detected immediately after the ink amount has reached the lower limit. The predetermined amount can be appropriately selected.
When a print job includes a large number of sheets, the amount of ink in the ink tank may become insufficient before printing of all the sheets is finished. Therefore, once a predetermined number of pixels is printed, the amount of ink remaining in the ink tank may be detected during a printing processing as well. In this case, the printing processing is interrupted by the detection. Thus, in the case of an ink jet recording apparatus which has ink tanks for multiple colors so that full-color images are formed, it is preferable to detect only the amount of ink in an ink tank for a specific color when the amount of ink used exceeds an amount corresponding to the predetermined number of pixels.
A tenth aspect of the present invention is an ink jet recording apparatus comprising: an ink jet recording head including an ink tank to which ink is supplied, the ink jet recording head printing by jetting the ink from the ink tank in accordance with image information in a print job; remaining ink amount detecting means for detecting the remaining ink amount for every predetermined number of printed pixels, which number of printed pixels is smaller than the number of pixels which can be printed after an empty signal indicating shortage of ink is outputted, and outputting the empty signal when the ink amount is no more than a lower limit; and ink supply means including a main tank for storing ink, the ink supply means supplying ink from the main tank to the ink tank in response to the empty signal outputted from the remaining ink amount detecting means.
The amount of ink remaining in the ink tank is detected when the ink amount reaches the lower limit. However, even after the remaining ink amount has reached the lower limit, some ink remains in the ink tank. According to the tenth aspect, the remaining ink amount detecting means detects the ink amount for every predetermined number of printed pixels, which predetermined number of printed pixels is smaller than the number of pixels which can be printed with the ink remaining in the ink tank after the remaining ink amount has reached the lower limit. In this way, a case in which ink in the ink tank runs out during printing so that further printing cannot be performed is prevented. The predetermined number of pixels for the ink amount detection is preferably set on the basis of the coverage area for the best quality. As a result, printing of files having a large coverage area can be ensured.
An eleventh aspect of the present invention is an ink jet recording apparatus comprising: an ink jet recording head including an ink tank to which ink is supplied, the ink jet recording head printing by jetting the ink from the ink tank in accordance with image information in a print job; remaining ink amount detecting means for controlling, when the print job is not being printed, the amount of ink remaining in the ink tank by a number of pixels corresponding to the amount of ink jetted from the ink jet recording head, and for detecting the remaining ink amount when the number of pixels exceeds a predetermined number, and outputting an empty signal indicating shortage of ink when the ink amount is no more than a lower limit; and ink supply means including a main tank for storing ink, the ink supply means supplying ink from the main tank to the ink tank in response to the empty signal outputted from the remaining ink amount detecting means.
When the amount of ink remaining in the ink tank is detected directly, the remaining ink amount can be more accurately detected as compared with cases in which the remaining ink amount is detected based on the number of pixels corresponding to the amount of ink jetted from the ink jet recording head. However, this direct detection takes time. Thus, according to the eleventh aspect, the detection mode is switched such that, the amount of ink remaining in the ink tank is initially detected based on the number of pixels corresponding to the amount of ink jetted from the ink jet recording head until the number of pixels jetted reaches a predetermined value, and then, after the number of pixels has reached the predetermined value, the amount of ink remaining in the ink tank is directly detected.
Namely, when the amount of ink remaining in the ink tank is relatively large, even if there is an error in the ink amount, the possibility of the ink running out is low. Thus, the ink amount is detected at high speed by calculating the jetted pixels. However, when the amount of ink remaining in the ink tank is relatively small, if there is an error in the remaining ink amount, ink may run out. Therefore, the remaining ink amount is accurately detected by detecting the amount of ink remaining in the ink tank directly. The structure for directly detecting the remaining ink amount is not particularly limited. For example, an optical sensor can be used in which the remaining ink amount is detected by irradiating light onto the level of the ink and measuring the time required for the light to be reflected back to the optical sensor.
By switching the detection mode in the above-described manner, the printing processing can be efficiently carried out. The predetermined number of pixels can be appropriately selected. It is advantageous if the predetermined number of pixels is set to a number of pixels which corresponds to the ink amount near the lower limit of the ink tank.
A twelfth aspect of the present invention is an ink jet recording apparatus comprising: an ink jet recording head including an ink tank to which ink is supplied, the ink jet recording head printing by jetting the ink from the ink tank in accordance with image information in a print job; remaining ink amount detecting means for detecting the amount of ink remaining in the ink tank at predetermined time intervals and after the ink is supplied, and outputting an empty signal indicating shortage of ink when the remaining ink amount is no more than a lower limit; ink supply means including a main tank for storing ink, the ink supply means supplying ink from the main tank to the ink tank in response to the empty signal outputted from the remaining ink amount detecting means; and control means which outputs a main tank empty signal indicating that the main tank is empty, when the remaining ink amount detecting means detects the ink amount remaining after ink supply and outputs the empty signal.
According to the twelfth aspect, the remaining ink amount detecting means detects the ink amount after ink has been supplied to the ink tank. When the remaining ink amount detecting means outputs the empty signal again, it is determined that ink has not been supplied to the ink tank and that there is no ink in the main tank. With this structure, the amount of ink in the main tank can be detected without using a sensor. Therefore, the apparatus as a whole can be produced at a low cost.
A thirteenth aspect of the present invention is an ink jet recording apparatus comprising: an ink jet recording head including an ink tank to which ink is supplied, the ink jet recording head printing by jetting the ink from the ink tank in accordance with image information in a print job; storage means for storing a number of pixels corresponding to the amount of ink jetted from the ink jet recording head; remaining ink amount detecting means for detecting the amount of ink remaining in the ink tank at predetermined time intervals and after ink supply, and outputting an empty signal indicating shortage of ink when the remaining ink amount is no more than a lower limit; and control means for comparing, when the remaining ink amount detecting means detects the remaining ink amount after the ink is supplied and outputs the empty signal, the number of pixels stored in the storage means with the number of pixels corresponding to the amount of ink filled in the main tank and outputting, when the numbers are the same or close to each other, a main tank empty signal indicating that the main tank is empty.
According to the thirteenth aspect, after ink has been supplied to the ink tank, the remaining ink amount detecting means detects the amount of ink remaining in the ink tank. When the remaining ink amount detecting means outputs the empty signal again, it can be determined that ink has not been supplied to the ink tank or an ink flow path between the main tank and the ink tank is being interrupted for some reason. Accordingly, the control means compares the number of pixels stored in the storage means with the number of pixels corresponding to the amount of ink filled in the main tank. When the numbers are the same or close to each other, it is determined that ink has not been supplied to the ink tank, and that the main tank is empty. Then, the control means outputs a main tank empty signal indicating that the main tank is empty. The ink jet recording apparatus may also be structured such that, when the number of pixels stored in the storage means is significantly different from the number of pixels corresponding to the amount of ink filled in the main tank (i.e. the amount of ink in the main tank before a print job), it is determined that the ink flow path between the main tank and the ink tank is interrupted, and a warning is given.
With the above-described structure, the amount of ink in the main tank can be detected without using a sensor. Therefore, the apparatus as a whole can be produced at a low cost. Further, problems caused by interruption of the ink flow from the tank or the like can also be found.
In the twelfth and thirteenth aspects, for example, in cases where an upper limit sensor is provided which outputs a signal when ink is not supplied to the ink tank to its upper limit, it can be determined that there is no ink in the main tank when the upper limit sensor outputs a signal after ink has been supplied to the ink tank. Alternatively, in cases where an upper limit sensor is provided which outputs a signal when ink which is supplied to the ink tank reaches its upper limit, it can be determined that there is no ink in the main tank when the upper limit sensor outputs no signal after ink has been supplied to the ink tank.